pub use OrderingOp::*;

use crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::{path_local, path_std, pathvec_std};

use rustc_ast::ptr::P;
use rustc_ast::{self as ast, BinOpKind, Expr, MetaItem};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::Span;

pub fn expand_deriving_partial_ord(
    cx: &mut ExtCtxt<'_>,
    span: Span,
    mitem: &MetaItem,
    item: &Annotatable,
    push: &mut dyn FnMut(Annotatable),
) {
    macro_rules! md {
        ($name:expr, $op:expr, $equal:expr) => {{
            let inline = cx.meta_word(span, sym::inline);
            let attrs = vec![cx.attribute(inline)];
            MethodDef {
                name: $name,
                generics: Bounds::empty(),
                explicit_self: borrowed_explicit_self(),
                args: vec![(borrowed_self(), sym::other)],
                ret_ty: Literal(path_local!(bool)),
                attributes: attrs,
                is_unsafe: false,
                unify_fieldless_variants: true,
                combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
                    cs_op($op, $equal, cx, span, substr)
                })),
            }
        }};
    }

    let ordering_ty = Literal(path_std!(cmp::Ordering));
    let ret_ty = Literal(Path::new_(
        pathvec_std!(option::Option),
        None,
        vec![Box::new(ordering_ty)],
        PathKind::Std,
    ));

    let inline = cx.meta_word(span, sym::inline);
    let attrs = vec![cx.attribute(inline)];

    let partial_cmp_def = MethodDef {
        name: sym::partial_cmp,
        generics: Bounds::empty(),
        explicit_self: borrowed_explicit_self(),
        args: vec![(borrowed_self(), sym::other)],
        ret_ty,
        attributes: attrs,
        is_unsafe: false,
        unify_fieldless_variants: true,
        combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
            cs_partial_cmp(cx, span, substr)
        })),
    };

    // avoid defining extra methods if we can
    // c-like enums, enums without any fields and structs without fields
    // can safely define only `partial_cmp`.
    let methods = if is_type_without_fields(item) {
        vec![partial_cmp_def]
    } else {
        vec![
            partial_cmp_def,
            md!(sym::lt, true, false),
            md!(sym::le, true, true),
            md!(sym::gt, false, false),
            md!(sym::ge, false, true),
        ]
    };

    let trait_def = TraitDef {
        span,
        attributes: vec![],
        path: path_std!(cmp::PartialOrd),
        additional_bounds: vec![],
        generics: Bounds::empty(),
        is_unsafe: false,
        supports_unions: false,
        methods,
        associated_types: Vec::new(),
    };
    trait_def.expand(cx, mitem, item, push)
}

#[derive(Copy, Clone)]
pub enum OrderingOp {
    PartialCmpOp,
    LtOp,
    LeOp,
    GtOp,
    GeOp,
}

pub fn some_ordering_collapsed(
    cx: &mut ExtCtxt<'_>,
    span: Span,
    op: OrderingOp,
    self_arg_tags: &[Ident],
) -> P<ast::Expr> {
    let lft = cx.expr_ident(span, self_arg_tags[0]);
    let rgt = cx.expr_addr_of(span, cx.expr_ident(span, self_arg_tags[1]));
    let op_sym = match op {
        PartialCmpOp => sym::partial_cmp,
        LtOp => sym::lt,
        LeOp => sym::le,
        GtOp => sym::gt,
        GeOp => sym::ge,
    };
    cx.expr_method_call(span, lft, Ident::new(op_sym, span), vec![rgt])
}

pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
    let test_id = Ident::new(sym::cmp, span);
    let ordering = cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::Equal]));
    let ordering_expr = cx.expr_path(ordering.clone());
    let equals_expr = cx.expr_some(span, ordering_expr);

    let partial_cmp_path = cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp]);

    // Builds:
    //
    // match ::std::cmp::PartialOrd::partial_cmp(&self_field1, &other_field1) {
    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) =>
    // match ::std::cmp::PartialOrd::partial_cmp(&self_field2, &other_field2) {
    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) => {
    // ...
    // }
    // cmp => cmp
    // },
    // cmp => cmp
    // }
    //
    cs_fold(
        // foldr nests the if-elses correctly, leaving the first field
        // as the outermost one, and the last as the innermost.
        false,
        |cx, span, old, self_f, other_fs| {
            // match new {
            //     Some(::std::cmp::Ordering::Equal) => old,
            //     cmp => cmp
            // }

            let new = {
                let other_f = match other_fs {
                    [o_f] => o_f,
                    _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
                };

                let args =
                    vec![cx.expr_addr_of(span, self_f), cx.expr_addr_of(span, other_f.clone())];

                cx.expr_call_global(span, partial_cmp_path.clone(), args)
            };

            let eq_arm = cx.arm(span, cx.pat_some(span, cx.pat_path(span, ordering.clone())), old);
            let neq_arm = cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));

            cx.expr_match(span, new, vec![eq_arm, neq_arm])
        },
        equals_expr,
        Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
            if self_args.len() != 2 {
                cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
            } else {
                some_ordering_collapsed(cx, span, PartialCmpOp, tag_tuple)
            }
        }),
        cx,
        span,
        substr,
    )
}

/// Strict inequality.
fn cs_op(
    less: bool,
    inclusive: bool,
    cx: &mut ExtCtxt<'_>,
    span: Span,
    substr: &Substructure<'_>,
) -> P<Expr> {
    let ordering_path = |cx: &mut ExtCtxt<'_>, name: &str| {
        cx.expr_path(
            cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, Symbol::intern(name)])),
        )
    };

    let par_cmp = |cx: &mut ExtCtxt<'_>, span, self_f: P<Expr>, other_fs: &[P<Expr>], default| {
        let other_f = match other_fs {
            [o_f] => o_f,
            _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
        };

        // `PartialOrd::partial_cmp(self.fi, other.fi)`
        let cmp_path = cx.expr_path(
            cx.path_global(span, cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp])),
        );
        let cmp = cx.expr_call(
            span,
            cmp_path,
            vec![cx.expr_addr_of(span, self_f), cx.expr_addr_of(span, other_f.clone())],
        );

        let default = ordering_path(cx, default);
        // `Option::unwrap_or(_, Ordering::Equal)`
        let unwrap_path = cx.expr_path(
            cx.path_global(span, cx.std_path(&[sym::option, sym::Option, sym::unwrap_or])),
        );
        cx.expr_call(span, unwrap_path, vec![cmp, default])
    };

    let fold = cs_fold1(
        false, // need foldr
        |cx, span, subexpr, self_f, other_fs| {
            // build up a series of `partial_cmp`s from the inside
            // out (hence foldr) to get lexical ordering, i.e., for op ==
            // `ast::lt`
            //
            // ```
            // Ordering::then_with(
            //    Option::unwrap_or(
            //        PartialOrd::partial_cmp(self.f1, other.f1), Ordering::Equal)
            //    ),
            //    Option::unwrap_or(
            //        PartialOrd::partial_cmp(self.f2, other.f2), Ordering::Greater)
            //    )
            // )
            // == Ordering::Less
            // ```
            //
            // and for op ==
            // `ast::le`
            //
            // ```
            // Ordering::then_with(
            //    Option::unwrap_or(
            //        PartialOrd::partial_cmp(self.f1, other.f1), Ordering::Equal)
            //    ),
            //    Option::unwrap_or(
            //        PartialOrd::partial_cmp(self.f2, other.f2), Ordering::Greater)
            //    )
            // )
            // != Ordering::Greater
            // ```
            //
            // The optimiser should remove the redundancy. We explicitly
            // get use the binops to avoid auto-deref dereferencing too many
            // layers of pointers, if the type includes pointers.

            // `Option::unwrap_or(PartialOrd::partial_cmp(self.fi, other.fi), Ordering::Equal)`
            let par_cmp = par_cmp(cx, span, self_f, other_fs, "Equal");

            // `Ordering::then_with(Option::unwrap_or(..), ..)`
            let then_with_path = cx.expr_path(
                cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::then_with])),
            );
            cx.expr_call(span, then_with_path, vec![par_cmp, cx.lambda0(span, subexpr)])
        },
        |cx, args| match args {
            Some((span, self_f, other_fs)) => {
                let opposite = if less { "Greater" } else { "Less" };
                par_cmp(cx, span, self_f, other_fs, opposite)
            }
            None => cx.expr_bool(span, inclusive),
        },
        Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
            if self_args.len() != 2 {
                cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
            } else {
                let op = match (less, inclusive) {
                    (false, false) => GtOp,
                    (false, true) => GeOp,
                    (true, false) => LtOp,
                    (true, true) => LeOp,
                };
                some_ordering_collapsed(cx, span, op, tag_tuple)
            }
        }),
        cx,
        span,
        substr,
    );

    match *substr.fields {
        EnumMatching(.., ref all_fields) | Struct(.., ref all_fields) if !all_fields.is_empty() => {
            let ordering = ordering_path(cx, if less ^ inclusive { "Less" } else { "Greater" });
            let comp_op = if inclusive { BinOpKind::Ne } else { BinOpKind::Eq };

            cx.expr_binary(span, comp_op, fold, ordering)
        }
        _ => fold,
    }
}